1. Field of the Invention
This invention relates to an electronically controlled fuel injection system for use in an internal combustion engine and, more particularly, to a simple and inexpensive fuel supply control system for determining an amount of fuel supplied to the engine in accordance with intake air flow.
2. Description of the Prior Art
It is common practice to use an electronic control system to control the amount of fuel supplied to an internal combustion engine in accordance with engine suction vacuum appearing in the intake passage downstream of the throttle valve. However, such practice cannot be applied to the case where an exhaust gas recirculation system is incorporated in such an engine in order to improve its exhaust emission characteristics, since changes of exhaust gas recirculation flow cause the engine suction vacuum to increase or decrease so as to produce a great divergence between the requisite and actual quantities of fuel supplied to the engine, resulting in poor fuel economy, exhaust emission characteristics and drivability. For this reason, the amount of fuel supplied to the engine has been controlled in accordance with intake air flow detected by an expensive air flow meter provided in the intake passage.
In recent years, accurate and inexpensive semiconductor pressure sensors have been in extensive use. Accordingly, it is advantageous in cost and accuracy to control the amount of fuel supplied to the engine in accordance with intake air flow derived from engine speed and engine suction vacuum and corrected in accordance with exhaust gas recirculation flow, using semiconductor pressure sensors to measure the engine suction vacuum and exhaust gas recirculation flow.